Force sensor array

ABSTRACT

An apparatus includes a force sensor circuit and a controller. The force sensor circuit includes first, second, third, and fourth electrodes disposed on a substrate. The first and second electrodes extend through first and second cells of a row of cells. The third and fourth electrodes extend through third and fourth cells of a column of cells. The first electrode occupies more area in the first cell than in the second cell. The second electrode occupies more area in the second cell than in the first cell. The third electrode occupies more area in the third cell than in the fourth cell. The fourth electrode occupies more area in the fourth cell than in the third cell. The controller detects a force and a position of the force based on signals communicated by the force sensor circuit.

TECHNICAL FIELD

This disclosure generally relates to force sensing technology.

BACKGROUND

According to an example scenario, a force sensor detects the presenceand position of a force applied within a force-sensitive area of a forcesensor array integrated within a display stack. In aforce-sensitive-display application, a force sensor array allows a userto interact directly with what is displayed on the screen, rather thanindirectly with a mouse or touch pad. A force sensor is attached to orprovided as part of a desktop computer, laptop computer, tabletcomputer, personal digital assistant (PDA), smartphone, satellitenavigation device, portable media player, portable game console, kioskcomputer, point-of-sale device, or other device. A control panel on ahousehold or other appliance may include a force sensor.

In one example, when an object physically applies a force to a screenwithin a force sensitive area of a force sensor of the screen (e.g., byphysically pressing a cover layer of the screen), a change incapacitance occurs within the screen at a position of the force sensorthat corresponds to the position of the object within the forcesensitive area of the force sensor. A force controller processes thechange in capacitance to determine the position of the change ofcapacitance within the force sensor (e.g., within a force sensor arrayof the force sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

For a more complete understanding of the present disclosure and itsadvantages, reference is made to the following descriptions, taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example system that includes a force sensor,according to an embodiment of the present disclosure;

FIG. 2 illustrates an example device that houses a force sensor,according to an embodiment of the present disclosure;

FIG. 3 illustrates an example mechanical stack of a device that includesa force sensor, according to an embodiment of the present disclosure;

FIG. 4 illustrates an example force sensing system, according to anembodiment of the present disclosure;

FIG. 5A illustrates an example force sensing array, according to anembodiment of the present disclosure;

FIG. 5B illustrates a cell of an example force sensing array, accordingto an embodiment of the present disclosure;

FIG. 6A illustrates an example force sensing system, according to anembodiment of the present disclosure;

FIG. 6B illustrates an example force sensing system, according to anembodiment of the present disclosure;

FIG. 7A illustrates an example force sensing array, according to anembodiment of the present disclosure;

FIG. 7B illustrates a cell of an example force sensing array, accordingto an embodiment of the present disclosure;

FIG. 8A illustrates an example force sensing array, according to anembodiment of the present disclosure; and

FIG. 8B illustrates a cell of an example force sensing array, accordingto an embodiment of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Certain devices include force sensors that can detect both the presenceand a position of an applied force. The force can be applied to thedevice, for example, by pressing an object such as a finger and/or astylus against the device. The force sensor can detect the positionand/or location of the force and in some instances the magnitude of theforce. The device then responds according to the location and themagnitude of the force. For example, a device may close an applicationif a large amount of force is applied to the device. As another example,the device may increase the contrast of a display if a small amount offorce is applied to a particular portion of the device.

Existing force sensors detect a force by implementing an array ofelectrodes. When a force is applied to the device, the electrodes thatare close to the applied force may experience a change in capacitancesuch as, for example, a change in mutual capacitance between theelectrodes or a change in self capacitance. That change in capacitancemay be detected by the device. The device may then process and respondto the detected force.

One challenge presented by existing force sensor arrays is the number oftracks used to couple the electrodes of the force sensor to a controllerof the device. In existing force sensors each electrode of the forcesensor couples to the controller through at least one track. Becauseexisting force sensors use numerous electrodes to implement forcesensing, the number of tracks is also numerous. The number of tracksresults in less available space in the device to house other components.As a result, a force sensor may lead to fewer features being implementedin the device. Furthermore, the number of tracks results in a highermanufacturing cost because the device uses more pins and, in someinstances, a dedicated force sensing system.

This disclosure contemplates a force sensor that can detect thepresence, magnitude, and position of an applied force. The force sensorimplements this force sensing using at most four electrodes. As aresult, only four tracks are used to couple the force sensor to acontroller. The reduced number of tracks increases the amount ofavailable space to implement other features and/or hardware in thedevice. Additionally, by using four electrodes, it may be possible toimplement the force sensor using the same controller and/or integratedcircuit as a touch sensor in the same device. The force sensor and thedevice will be described in more detail using FIGS. 1 through 8B. Thedevice will be described generally using FIGS. 1 through 3. FIG. 4 willdescribe existing force sensor implementations. The contemplated forcesensor will be described in more detail using FIGS. 5A through 8B.

FIG. 1 illustrates an example system 100 that includes a force sensor102, according to an embodiment of the present disclosure. Force sensor102 includes force sensor array 106 and force controller 108. Forcesensor array 106 and force controller 108 detect the presence andposition of a force within a force-sensitive area of force sensor array106.

Force sensor array 106 includes one or more force-sensitive areas. Inone embodiment, force sensor array 106 includes an array of electrodesdisposed on one or more substrates, which are made of a dielectricmaterial. Reference to a force sensor array can encompass both theelectrodes of force sensor array 106 and the substrate(s) on which theyare disposed. Alternatively, reference to a force sensor array mayencompass the electrodes of force sensor array 106, but not thesubstrate(s) on which they are disposed.

In one embodiment, an electrode is an area of conductive materialforming a shape, such as for example a disc, square, rectangle, thinline, other shape, or a combination of these shapes. One or more cuts inone or more layers of conductive material (at least in part) create theshape of an electrode, and the area of the shape are (at least in part)bounded by those cuts. In one embodiment, the conductive material of anelectrode occupies approximately 100% of the area of its shape. Forexample, an electrode is made of indium tin oxide (ITO) and the ITO ofthe electrode occupies approximately 100% of the area of its shape(sometimes referred to as 100% fill). In one embodiment, the conductivematerial of an electrode occupies less than 100% of the area of itsshape. For example, an electrode may be made of fine lines of metal orother conductive material (FLM), such as for example copper, silver, ora copper- or silver-based material, and the fine lines of conductivematerial may occupy approximately 5% of the area of its shape in ahatched, mesh, or other pattern. Reference to FLM encompasses suchmaterial. In one embodiment, an electrode is made of flexible printedcircuit (FPC) type material (e.g., solid coppers areas on one or twolayers/surfaces of a substrate). Although this disclosure describes orillustrates particular electrodes made of particular conductive materialforming particular shapes with particular fill percentages havingparticular patterns, this disclosure contemplates, in any combination,electrodes made of other conductive materials forming other shapes withother fill percentages having other patterns.

The shapes of the electrodes (or other elements) of a force sensor array106 constitute, in whole or in part, one or more macro-features of forcesensor array 106. One or more characteristics of the implementation ofthose shapes (such as, for example, the conductive materials, fills, orpatterns within the shapes) constitute in whole or in part one or moremicro-features of force sensor array 106. One or more macro-features ofa force sensor array 106 may determine one or more characteristics ofits functionality, and one or more micro-features of force sensor array106 may determine one or more optical features of force sensor array106, such as transmittance, refraction, or reflection.

Although this disclosure describes a number of example electrodes, thepresent disclosure is not limited to these example electrodes and otherelectrodes may be implemented. Additionally, although this disclosuredescribes a number of example embodiments that include particularconfigurations of particular electrodes forming particular nodes, thepresent disclosure is not limited to these example embodiments and otherconfigurations may be implemented. In one embodiment, a number ofelectrodes are disposed on the same or different surfaces of the samesubstrate. Additionally or alternatively, different electrodes may bedisposed on different substrates. Although this disclosure describes anumber of example embodiments that include particular electrodesarranged in specific, example patterns, the present disclosure is notlimited to these example patterns and other electrode patterns may beimplemented.

A mechanical stack contains the substrate (or multiple substrates) andthe conductive material forming the electrodes of force sensor array106. For example, the mechanical stack may include a first layer ofoptically clear adhesive (OCA) beneath a cover panel. The cover panelmay be clear and made of a resilient material, such as for exampleglass, polycarbonate, or poly(methyl methacrylate) (PMMA). Thisdisclosure contemplates cover panel being made of any material. Thefirst layer of OCA may be disposed between the cover panel and thesubstrate with the conductive material forming the electrodes. Themechanical stack may also include a second layer of OCA and a dielectriclayer (which may be made of PET or another material, similar to thesubstrate with the conductive material forming the electrodes). As analternative, a thin coating of a dielectric material may be appliedinstead of the second layer of OCA and the dielectric layer. The secondlayer of OCA may be disposed between the substrate with the conductivematerial making up the electrodes and the dielectric layer, and thedielectric layer may be disposed between the second layer of OCA and anair gap to a display of a device including force sensor array 106 andforce controller 108. For example, the cover panel may have a thicknessof approximately 1 millimeter (mm); the first layer of OCA may have athickness of approximately 0.05 mm; the substrate with the conductivematerial forming the electrodes may have a thickness of approximately0.05 mm; the second layer of OCA may have a thickness of approximately0.05 mm; and the dielectric layer may have a thickness of approximately0.05 mm.

Although this disclosure describes a particular mechanical stack with aparticular number of particular layers made of particular materials andhaving particular thicknesses, this disclosure contemplates othermechanical stacks with any number of layers made of any materials andhaving any thicknesses. For example, in one embodiment, a layer ofadhesive or dielectric may replace the dielectric layer, second layer ofOCA, and air gap described above, with there being no air gap in thedisplay.

One or more portions of the substrate of force sensor array 106 may bemade of polyethylene terephthalate (PET) or another material. Thisdisclosure contemplates any substrate with portions made of anymaterial(s). In one embodiment, one or more electrodes in force sensorarray 106 are made of ITO in whole or in part. Additionally oralternatively, one or more electrodes in force sensor array 106 are madeof fine lines of metal or other conductive material. For example, one ormore portions of the conductive material may be copper or copper-basedand have a thickness of approximately 5 microns (μm) or less and a widthof approximately 10 μm or less. As another example, one or more portionsof the conductive material may be silver or silver-based and similarlyhave a thickness of approximately 5 μm or less and a width ofapproximately 10 μm or less. This disclosure contemplates any electrodesmade of any materials.

In one embodiment, force sensor array 106 implements a capacitive formof force sensing. In a mutual-capacitance implementation, force sensorarray 106 may include an array of drive and sense electrodes forming anarray of capacitive nodes. A drive electrode and a sense electrode mayform a capacitive node. The drive and sense electrodes forming thecapacitive node are positioned near each other but do not makeelectrical contact with each other. Instead, in response to a signalbeing applied to the drive electrodes for example, the drive and senseelectrodes capacitively couple to each other across a space betweenthem. A pulsed or alternating voltage applied to the drive electrode (byforce controller 108) induces a charge on the sense electrode, and theamount of charge induced is susceptible to external influence (such as aforce or the proximity of an object). The drive and sense electrodes areseparated by a flexible material that compresses when a force is appliedto the material. When an object presses or applies a force withinproximity of the capacitive node, the material compresses and thedistance between the drive and sense electrodes proximate the capacitivenode decreases resulting in a change in capacitance the capacitive node.Force controller 108 measures the change in capacitance. By measuringchanges in capacitance throughout the array, force controller 108determines the position of the force or proximity within force-sensitiveareas of force sensor array 106.

In a self-capacitance implementation, force sensor array 106 may includean array of electrodes of a single type that may each form a capacitivenode. When an object applies a force within proximity of the capacitivenode, a change in self-capacitance may occur at the capacitive node andforce controller 108 measures the change in capacitance, for example, asa change in the amount of charge implemented to raise the voltage at thecapacitive node by a predetermined amount. As with a mutual-capacitanceimplementation, by measuring changes in capacitance throughout thearray, force controller 108 determines the position of the force orproximity within force-sensitive areas of force sensor array 106. Thisdisclosure contemplates any form of capacitive force sensing.

In one embodiment, force sensor array 106 includes electrodes disposedin a pattern on one side of a single substrate. In such a configuration,a pair of electrodes capacitively coupled to each other across a spacebetween them form a capacitive node. As an example self-capacitanceimplementation, electrodes of a single type are disposed in a pattern ona single substrate. In addition or as an alternative to havingelectrodes disposed in a pattern on one side of a single substrate,force sensor array 106 may have electrodes disposed in a pattern on oneside of a substrate and electrodes disposed in a pattern on another sideof the substrate. In such configurations, an intersection of electrodesforms a capacitive node. Such an intersection may be a position wherethe electrodes “cross” or come nearest each other in their respectiveplanes. The electrodes do not make electrical contact with eachother—instead they are capacitively coupled to each other across adielectric at the intersection. Although this disclosure describesparticular configurations of particular electrodes forming particularnodes, this disclosure contemplates other configurations of electrodesforming nodes. Moreover, this disclosure contemplates other electrodesdisposed on any number of substrates in any patterns.

As described above, a change in capacitance at a capacitive node offorce sensor array 106 may indicate a force input at the position of thecapacitive node. Force controller 108 detects and processes the changein capacitance to determine the presence and position of the force orproximity input. In one embodiment, force controller 108 thencommunicates information about the force or proximity input to one ormore other components (such as one or more central processing units(CPUs)) of a device that includes force sensor array 106 and forcecontroller 108, which may respond to the force or proximity input byinitiating a function of the device (or an application running on thedevice). Although this disclosure describes a particular forcecontroller 108 having particular functionality with respect to aparticular device and a particular force sensor 102, this disclosurecontemplates other force controllers having any functionality withrespect to any device and any force sensor.

In one embodiment, force controller 108 is implemented as one or moreintegrated circuits (ICs), such as for example general-purposemicroprocessors, microcontrollers, programmable logic devices or arrays,application-specific ICs (ASICs). Force controller 108 comprises anycombination of analog circuitry, digital logic, and digital non-volatilememory. In one embodiment, force controller 108 is disposed on aflexible printed circuit (FPC) bonded to the substrate of force sensorarray 106, as described below. The FPC may be active or passive. In oneembodiment, multiple force controllers 108 are disposed on the FPC.

In an example implementation, force controller 108 includes a processorunit, a drive unit, a sense unit, and a storage unit. In such animplementation, the drive unit supplies drive signals to the driveelectrodes of force sensor array 106, and the sense unit senses chargeat the capacitive nodes of force sensor array 106 and providesmeasurement signals to the processor unit representing capacitances atthe capacitive nodes. The processor unit controls the supply of drivesignals to the drive electrodes by the drive unit and processesmeasurement signals from the sense unit to detect and process thepresence and position of a force or proximity input withinforce-sensitive areas of force sensor array 106. The processor unit mayalso track changes in the position of a force or proximity input withinforce-sensitive areas of force sensor array 106. The storage unit storesprogramming for execution by the processor unit, including programmingfor controlling the drive unit to supply drive signals to the driveelectrodes, programming for processing measurement signals from thesense unit, and other programming. Although this disclosure describes aparticular force controller 108 having a particular implementation withparticular components, this disclosure contemplates force controllerhaving other implementations with other components.

Tracks 110 of conductive material disposed on the substrate of forcesensor array 106 couple the electrodes of force sensor array 106 toconnection pads 112, also disposed on the substrate of force sensorarray 106. As described below, connection pads 112 facilitate couplingof tracks 110 to force controller 108. Tracks 110 may extend into oraround (e.g., at the edges of) force-sensitive areas of force sensorarray 106. In one embodiment, particular tracks 110 provide connectionsfor coupling force controller 108 to electrodes of force sensor array106. Tracks 110 are made of fine lines of metal or other conductivematerial. For example, the conductive material of tracks 110 may becopper or copper-based and have a width of approximately 100 μm or less.As another example, the conductive material of tracks 110 may be silveror silver-based and have a width of approximately 100 μm or less. In oneembodiment, tracks 110 are made of ITO in whole or in part in additionor as an alternative to the fine lines of metal or other conductivematerial. Although this disclosure describes particular tracks made ofparticular materials with particular widths, this disclosurecontemplates tracks made of other materials and/or other widths. Inaddition to tracks 110, force sensor array 106 may include one or moreground lines terminating at a ground connector (which may be aconnection pad 112) at an edge of the substrate of force sensor array106 (similar to tracks 110).

Connection pads 112 may be located along one or more edges of thesubstrate, outside a force-sensitive area of force sensor array 106. Asdescribed above, force controller 108 may be on an FPC. Connection pads112 may be made of the same material as tracks 110 and may be bonded tothe FPC using an anisotropic conductive film (ACF). In one embodiment,connection 114 includes conductive lines on the FPC coupling forcecontroller 108 to connection pads 112, in turn coupling force controller108 to tracks 110 and to the drive or sense electrodes of force sensorarray 106. In another embodiment, connection pads 112 are connected toan electro-mechanical connector (such as, for example, a zero insertionforce wire-to-board connector). Connection 114 may or may not include anFPC. This disclosure contemplates any connection 114 between forcecontroller 108 and force sensor array 106.

FIG. 2 illustrates an example device 200 that houses force sensor 102,according to an embodiment of the present disclosure. Device 200 is anypersonal digital assistant, cellular telephone, smartphone, tabletcomputer, and the like. In one embodiment, device 200 includes othertypes of devices, such as automatic teller machines (ATMs), homeappliances, personal computers, and any other such device having a forcescreen. In the illustrated example, components of system 100 areinternal to device 200. Although this disclosure describes a particulardevice 200 having a particular implementation with particularcomponents, this disclosure contemplates any device 200 having anyimplementation with any components.

A particular example of device 200 is a smartphone that includes ahousing 201 and a force screen display 202 occupying a portion of asurface 204 of housing 201 of device 200. In an embodiment, housing 201is an enclosure of device 200, which may contain internal components(e.g., internal electrical components) of device 200. Force sensor 102may be coupled, directly or indirectly, to housing 201 of device 200.Display 202 may occupy a significant portion or all of a surface 204(e.g., one of the largest surfaces 204) of housing 201 of device 200.Reference to a display 202 includes cover layers that overlay the actualdisplay and force sensor elements of device 200. In the illustratedexample, surface 204 is a surface of the top cover layer of display 202.In an embodiment, the top cover layer (e.g., a glass cover layer) ofdisplay 202 is considered part of housing 201 of device 200.

In one embodiment, the large size of display 202 allows the display 202to present a wide variety of data, including a keyboard, a numerickeypad, program or application icons, and various other interfaces. Inone embodiment, a user interacts with device 200 by pressing/touchingdisplay 202 with a stylus, a finger, or any other object in order tointeract with device 200 (e.g., select a program for execution or totype a letter on a keyboard displayed on the display 202). In oneembodiment, a user interacts with device 200 using multiplepresses/touches to perform various operations, such as to zoom in orzoom out when viewing a document or image. In some embodiments, such ashome appliances, display 202 does not change or changes only slightlyduring device operation, and recognizes only single presses/touches.

Users may interact with device 200 by physically impacting surface 204(or another surface) of housing 201 of device 200, shown as impact 206,using an object 208, such as, for example, one or more fingers, one ormore styluses, or other objects. In one embodiment, surface 204 is acover layer that overlies display 202.

Device 200 includes buttons 210, which may perform any purpose inrelation to the operation of device 200. One or more of buttons 210(e.g., button 210 b) may operate as a so-called “home button” that, atleast in part, indicates to device 200 that a user is preparing toprovide input to force sensor 102 of device 200. As described in greaterdetail below, an embodiment of the present disclosure may reduce oreliminate various reasons for including a “home button.”

FIG. 3 illustrates an example mechanical stack 300 of a device thatincludes a force sensor according to an embodiment of the presentdisclosure. As illustrated in FIG. 3, mechanical stack 300 includes atouch sensor array 305, a display 202, a cushion 310, a force sensorarray 106, a protective layer 315, a cushion 320, and a chassis 625. Itis understood that mechanical stack 300 is an example and that thisdisclosure contemplates a mechanical stack that includes more or fewerlayers than those shown in FIG. 3. For example, a mechanical stack mayexclude touch sensor array 305. Furthermore, this disclosurecontemplates the layers of mechanical stack 300 being arranged in anyparticular order.

Touch sensor array 305 implements touch sensing capabilities of thedevice. In particular embodiments, touch sensor array 305 includeselectrodes configured to capacitively couple to one another to implementtouch sensing capabilities of the device. Using touch sensor array 305,the device can detect the presence and location of an object touchingtouch sensor array 305 and/or of an object within proximity of touchsensor array 305. The electrodes of touch sensor array 305 are coupledby tracks to a touch sensor controller of the device. In certainembodiments, the touch sensor controller and force controller 108 areimplemented in the same hardware and/or physical controller. Forexample, the device may use one controller to implement both forcecontroller 108 and the touch sensor controller. In some embodiments,force controller 108 and touch sensor controller are implemented inseparate hardware and/or controllers.

Cushion 310 is positioned between display 202 and force sensor array106. Cushion 310 prevents display 202 from directly contacting forcesensor array 106 and/or from interfering with force sensor array 106. Insome embodiments, cushion 310 is formed from a dielectric material thatelectrically shields force sensor array 106 from display 202. Cushion310 may be any appropriate thickness such as, for example, 200 microns.

Force sensor array 106 implements the force sensing capabilities of thedevice. Force sensor array 106 includes one or more electrodes 312disposed on a substrate 314. Electrodes 312 can be used to determine thepresence, magnitude, and location of a force applied to mechanical stack300. Particular designs for force sensor array 106 will be described inmore detail using FIGS. 4 through 8B. This disclosure contemplates forcesensor array 106 having any appropriate thickness such as, for example,25 microns.

Protective layer 315 is any material that separates force sensor array106 from cushion 320 in chassis 625. In one embodiment, protective layer315 includes a rigid material such as a cement that protects forcesensor array 106 from directly contacting cushion 320 and chassis 625.This disclosure contemplates protective layer 315 being of anyappropriate thickness such as, for example, 80 microns.

Cushion 320 is any flexible material that supports protective layer 315and force sensor array 106. This disclosure contemplates cushion 320being any appropriate thickness such as, for example, 400 microns. Whena force is applied to mechanical stack 300, cushion 320 may compress. Asa result, the distance between force sensor array 106 and chassis 625may decrease. As a result of that decrease, the capacitance between theelectrodes 312 of force sensor array 106 and chassis 625 changes. Forcecontroller 108 can detect that change in capacitance and determine thata force is being applied to mechanical stack 300.

Chassis 625 operates as a ground layer for mechanical stack 300. In oneembodiment, chassis 625 also supports the other layers of mechanicalstack 300. A capacitance between the electrodes 312 of force sensorarray 106 and chassis 625 is monitored by force controller 108.

FIG. 4 illustrates an example force sensing system 400 according to anembodiment of the present disclosure. As illustrated in FIG. 4, forcesensing system 400 includes touch sensor array 106 and force controller108. Force sensor array 106 is coupled to force controller 108 by tracks110. Force sensor array 106 and force controller 108 are configured todetect the presence, magnitude and location of a force applied on forcesensor array 106.

Force sensor array 106 includes one or more electrodes 405. Asillustrated in FIG. 4, each electrode 405 is positioned within forcesensor array 106. Each electrode 405 can be used to detect a forceapplied within the proximity of the electrode 405. When a force isapplied within proximity to an electrode 405, a capacitance associatedwith that electrode 405 changes. Force controller 108 can detect thatchange in capacitance and determine that a force is applied withinproximity to that electrode 405.

As illustrated in FIG. 4, each electrode 405 is coupled to forcecontroller 108 by a track 110. The example force sensor array 106includes nine electrodes 405. As a result, there are nine tracks 110coupling electrodes 405 to force controller 108. As the size of forcesensor array 106 grows and/or as the number of electrodes 405 increases,the number of tracks 110 also increase. The number of tracks 110decreases the amount of space available in a device to implement otherfeatures and/or hardware. By reducing the number of tracks 110,additional features and/or hardware can be implemented in the device.

This disclosure contemplates particular designs and patterns forelectrodes 405 that reduce the number of tracks 110. In one embodiment,a design and/or pattern for electrodes 405 reduces the number of tracks110 to four tracks. Furthermore, only four electrodes 405 are used todetect the presence, magnitude, and location of a force applied to forcesensor array 106. These designs and patterns for electrodes 405 will bedescribed in more detail using FIGS. 5A through 8B.

FIG. 5A illustrates an example force sensing array 106 according to anembodiment of the present disclosure. As illustrated in FIG. 5A, forcesensing array 106 includes four electrodes: 505, 510, 515 and 520. Theelectrodes 505, 510, 515 and 520 are configured in a particular patternacross force sensing array 106. In one embodiment, by using this patternof electrodes 505, 510, 515 and 520, force sensing array 106 can detectthe presence, magnitude, and location of a force applied to forcesensing array 106 using only four electrodes.

The electrodes 505, 510, 515 and 520 are configured such that forcesensing array 106 can be divided into a grid of cells 525A through 525Y.Each cell includes a portion of electrodes 505, 510, 515 and 520. Thedensities of electrodes 505, 510, 515 and/or 520 changes from cell tocell. For example, in cell 525A, electrodes 510 and 520 occupy smallerareas than electrodes 505 and 515. In cell 525M, electrodes 515 and 520occupy substantially the same area and electrodes 505 and 510 occupysubstantially the same area.

In one embodiment, by varying the densities of the electrodes 505, 510,515 and 520 across the cells 525A through 525Y, it becomes possible todetect a location of a force applied to force sensing array 106 byanalyzing a ratio of the signals communicated by electrodes 505, 510,515 and 520. In the illustrated example of FIG. 5A, the area of a celloccupied by electrode 505 increases from the bottom of array 106 to thetop of array 106 while the area of a cell occupied by electrode 510increases from the top of array 106 to the bottom of array 106.Similarly, the area of a cell occupied by electrode 515 increases fromthe left of array 106 to the right of array 106 while the area of a celloccupied by electrode 520 increases from the right of array 106 to theleft of array 106. If a force is applied to cell 525A, then the signalcommunicated by electrode 505 is expected to be larger than the signalcommunicated by electrode 510 because electrode 505 occupies a largerarea in cell 525A than electrode 510. Likewise, the signal communicatedby electrode 515 is expected to be larger than the signal communicatedby electrode 520. In contrast, if the force is instead applied to cell525M, then the signal communicated by electrode 505 is expected to besubstantially the same as the signal communicated by electrode 510because electrode 505 occupies substantially the same area in cell 525Mas electrode 510. Likewise, the signal communicated by electrode 515 isexpected to be substantially the same as the signal communicated byelectrode 520. By determining the ratio between the signals communicatedby electrode 505 and electrode 510 and the ratio between the signalscommunicated by electrode 515 and electrode 520, force controller 108can determine which cell is the cell on which a force is applied. In oneembodiment, each cell of force sensing array 106 includes only fourelectrodes: 505, 510, 515 and 520. Furthermore, the cells 525A through525Y are of substantially equal size (e.g., within 1% difference inarea).

In one embodiment, each of the electrodes 505, 510, 515 and 520 includea plurality of fingers extending from a body. By varying the length ofthe fingers extending from the body, the density of the electrodes in acell can be varied. For example, in the first row of cells 525A through525E, the fingers of electrode 515 become shorter from cell 525A to cell525E. In contrast, the fingers of electrode 520 increase in length fromcell 525A to cell 525E.

In one embodiment, electrodes 505, 510, 515 and 520 determine differenttypes of position of an applied force. For example, force controller 108uses electrodes 505 and 510 to determine a vertical position of anapplied force, and force controller 108 uses electrodes 515 and 520 todetermine a horizontal position of the applied force. If a ratio betweenthe signals communicated by electrodes 515 and 520 are substantially thesame, then force controller 108 determines that the force is applied onthe column of cells 525C, 525H, 525M, 525R and 525W. If a ratio betweenthe signals communicated by electrode 505 and electrode 510 is large,then force controller 108 determines that the force is applied on therow of cells 525A through 525E. As a result of these two determinations,force controller 108 determines that the force is applied on cell 525C.

In one embodiment, the electrodes 505, 510, 515, and 520 are balancedacross force sensing array 106. For example, electrodes 505 and 510 maybe configured to occupy substantially the same amount of area aselectrodes 515 and 520 across force sensing array 106. As anotherexample, electrodes 505 and 510 may occupy the same amount of area thatelectrodes 515 and 520 occupy across a row of cells. This disclosurecontemplates balancing the electrodes 505, 510, 515, and 520 in anyappropriate manner. For example, the electrodes 505, 510, 515, and 520can be balanced by adjusting the thicknesses of the electrodes 505, 510,515, and 520. As another example, the electrodes 505, 510, 515, and 520can be balanced by adjusting the number of fingers of each electrode505, 510, 515, and 520. The fingers will be discussed in more detailusing subsequent figures.

FIG. 5B illustrates a cell 525M of an example force sensing array 106according to an embodiment of the present disclosure. As illustrated inFIG. 5B, cell 525M includes four electrodes 505, 510, 515, and 520. Eachelectrode 505, 510, 515, and 520 includes a plurality of fingersextending from a body of the electrode. For example, electrode 505includes a body 530 and one or more fingers 535 extending from body 530.Likewise, electrode 510 includes a body 530 and one or more fingers 535extending from the body. Electrodes 515 and 520 also include a body 530and one or more fingers 535 extending from the body. In certainembodiments, by varying the length of fingers 535 the density ofelectrodes 505, 510, 515, and 520 is varied.

Electrodes 505, 510, 515 and 520 may be configured to detect an appliedforce using only four tracks. In one embodiment, electrodes 505, 510,515, and 520 are disposed on opposing surfaces of a substrate. Forexample, electrodes 505 and 510 are disposed on a top surface of thesubstrate and electrodes 505 and 510 are disposed on a bottom surface ofthe substrate.

FIGS. 6A and 6B illustrate an example force sensing system according toan embodiment of the present disclosure. FIG. 6A illustrates a firstsurface of a substrate and FIG. 6B illustrates a second surface of thesubstrate. Electrodes 515 and 520 are disposed on the first surface ofthe substrate and electrodes 505 and 510 are disposed on the secondsurface of the substrate. These two surfaces of the substrate may beopposite each other. For example, electrodes 505 and 510 may be disposedon a top surface of the substrate 314 and electrodes 515 and 520 may bedisposed on a bottom surface of the substrate 314.

By disposing electrodes 505 and 510 and electrodes 515 and 520 ondifferent surfaces of the substrate, space is provided to run tracks 110to each of electrodes 505, 510, 515, and 520. The tracks for oneelectrode do not intersect with another electrode or another set oftracks 110. Furthermore, portions of electrodes 515 and 520 may also becoupled by extensions to other portions of those electrodes 515 and 520.In the illustrated example of FIG. 6A, portions of electrode 515 arecoupled such that electrode 515 extends through each of the cells offorce sensing array 106. Furthermore, electrode 520 is similarlyextended through the cells of force sensing array 106 so that theportions of electrode 520 are coupled together.

In this manner, only four electrodes 505, 510, 515, and 520 are neededto detect the presence, magnitude and location of a force applied toforce sensing array 106. Each electrode is coupled to a track 110 thatcarries signals from the electrodes to force controller 108. Forcecontroller 108 analyzes signals communicated by the electrodes throughtracks 110 to determine the presence, magnitude, and location of a forceapplied to force sensing array 106 (as described above). As a result,additional space is available in a device to implement other featuresand/or hardware.

In one embodiment, electrodes 505, 510, 515, and 520 are implemented onthe same surface of substrate 314. Vias and/or dielectric material isplaced at the intersections of electrodes 505, 510, 515, and 520 andintersections between tracks 110 to prevent electrical contact.

FIGS. 7A, 7B, 8A, and 8B show other contemplated designs and patternsfor electrodes 505, 515, 510, and 520 across force sensing array 106.For each design, this disclosure contemplates the electrodes beingdisposed on opposing surfaces of a substrate and/or the same surface ofthe substrate.

FIG. 7A illustrates an example force sensing array 106 according to anembodiment of the present disclosure. As shown in FIG. 7A, electrodes505, 510, 515, and 520 are arranged in a square or grid-like pattern. Inthis pattern, each electrode pair, for example electrodes 505 and 510and electrodes 515 and 520, occupy substantially the same area withineach cell. As with previously described designs, each electrode includesa plurality of fingers extending from a body. The length of thesefingers vary across force sensing array 106. As a result, a ratio of thesignals communicated by the electrodes will change depending on whichportion of force sensing array 106 is closest to an applied force.

FIG. 7B illustrates a cell 700 of an example force sensing array 106according to an embodiment of the present disclosure. As illustrated inFIG. 7B, cell 700 includes electrodes 505, 510, 515, and 520. Each ofthese electrodes extends through cell 700. Furthermore, in theillustrated example of FIG. 7B, the fingers of each electrode pair, forexample electrodes 505 and 510 and electrodes 515 and 520, aresubstantially the same length. However, for different cells of forcesensing array 106, these fingers may have different lengths.

FIG. 8A illustrates an example force sensing array 106 according to anembodiment of the present disclosure. As illustrated in FIG. 8A, forcesensing array 106 includes electrodes 505, 510, 515, and 520 arranged ina diamond pattern. Each of the electrodes includes a plurality offingers extending from a body. The lengths of these fingers may varyacross force sensing array 106. As a result, a ratio of the signalscommunicated by the electrodes will vary depending on the location of anapplied force on force sensing array 106.

FIG. 8B illustrates a cell 800 of an example force sensing array 106according to an embodiment of the present disclosure. As illustrated inFIG. 8B, cell 800 includes electrodes 505, 510, 515, and 520. Each ofthese electrodes extends through cell 800. Furthermore, in theillustrated example of FIG. 8B, each of the fingers of electrodes 505,510, 515, and 520 are substantially the same length. However, differentcells of force sensing array 106 may have different lengths for thesefingers and/or a different number of fingers.

In one embodiment, an apparatus includes a force sensor circuit and acontroller. The substrate includes first, second, third, and fourthelectrodes. The first electrode is disposed on the substrate and extendsthrough first and second cells of a row of cells. The first and secondcells are of substantially equal size and the first electrode occupiesmore area in the first cell than the first electrode occupies in thesecond cell. The second electrode is disposed on the substrate andextends through the first and second cells. The second electrodeoccupies more area in the second cell than the second electrode occupiesin the first cell. The third electrode is disposed on the substrate andextends through third and fourth cells of a column of cells. The thirdand fourth cells are of substantially equal size and the third electrodeoccupies more area in the third cell than the third electrode occupiesin the fourth cell. The fourth electrode is disposed on the substrateand extends through the third and fourth cells. The fourth electrodeoccupies more area in the fourth cell than the fourth electrode occupiesin the third cell. The controller detects a force and a position of theforce based on signals communicated by the force sensor circuit. In oneembodiment, the apparatus further includes a first track coupled to thefirst electrode, a second track coupled to the second electrode, a thirdtrack coupled to the third electrode, and a fourth track coupled to thefourth electrode. In one embodiment, the controller detects the positionof the force based on a first ratio of a first signal of the firstelectrode and a second signal of the second electrode and a second ratioof a third signal of the third electrode and a fourth signal of thefourth electrode. In one embodiment, each of the first, second, third,and fourth electrodes comprise a plurality of fingers extending from abody. In one embodiment, a first finger of the plurality of fingers ofthe first electrode is a different length than a second finger of theplurality of fingers of the first electrode and the first finger is inthe first cell and the second finger is in the second cell. In oneembodiment, the controller determines a horizontal position of the forcebased on signals of the first and second electrodes of the first celland a vertical position of the force based on signals of the third andfourth electrodes of the third cell. In one embodiment, the first andsecond electrodes of the first cell are disposed on a first surface ofthe substrate and the third and fourth electrodes of the first cell aredisposed on a second surface of the substrate. In one embodiment, thefirst cell contains only four electrodes. In one embodiment, the firstand second electrodes occupy substantially the same amount of area asthe third and fourth electrodes. In one embodiment, an amount of areaoccupied by the first and second electrodes in the row of cells issubstantially the same amount of area occupied by the third and fourthelectrodes in the column of cells

In one embodiment, a force sensor includes a substrate, a firstelectrode, a second electrode, a third electrode, and a fourthelectrode. The first electrode is disposed on the substrate and extendsthrough first and second cells of a row of cells. The first and secondcells being of substantially equal size, and the first electrodeoccupies more area in the first cell than the first electrode occupiesin the second cell. The second electrode is disposed on the substrateand extends through the first and second cells. The second electrodeoccupies more area in the second cell than the second electrode occupiesin the first cell. The third electrode is disposed on the substrate andextends through third and fourth cells of a column of cells. The thirdand fourth cells being of substantially equal size, and the thirdelectrode occupies more area in the third cell than the third electrodeoccupies in the fourth cell. The fourth electrode is disposed on thesubstrate and extends through the third and fourth cells. The fourthelectrode occupies more area in the fourth cell than the fourthelectrode occupies in the third cell. In one embodiment, the first andsecond electrodes extend through the third and fourth cells and thethird and fourth electrodes extend through the first and second cells.In one embodiment, the force sensor includes a first track coupled tothe first electrode, a second track coupled to the second electrode, athird track coupled to the third electrode, and a fourth track coupledto the fourth electrode. In one embodiment, each of the first, second,third, and fourth electrodes include a plurality of fingers extendingfrom a body. In one embodiment, a first finger of the plurality offingers of the first electrode is a different length than a secondfinger of the plurality of fingers of the first electrode and the firstfinger is in the first cell and the second finger is in the second cell.In one embodiment, the first and second electrodes are disposed on afirst surface of the substrate and the third and fourth electrodes ofthe first cell are disposed on a second surface of the substrate. In oneembodiment, the first cell contains only four electrodes. In oneembodiment, the first and second electrodes occupy substantially thesame amount of area on the substrate as the third and fourth electrodes.In one embodiment, an amount of area occupied by the first and secondelectrodes in the row of cells is substantially the same amount of areaoccupied by the third and fourth electrodes in the column of cells.

In one embodiment, an apparatus includes a force sensor circuit, acontroller, and first, second, third, and fourth tracks. The forcesensor circuit includes a substrate and first, second, third, and fourthelectrodes. The first electrode is disposed on the substrate and extendsthrough first and second cells of a row of cells. The first and secondcells being of substantially equal size, and the first electrodeoccupies more area in the first cell than the first electrode occupiesin the second cell. The second electrode is disposed on the substrateand extends through the first and second cells. The second electrodeoccupies more area in the second cell than the second electrode occupiesin the first cell. The third electrode is disposed on the substrate andextends through third and fourth cells of a column of cells. The thirdand fourth cells being of substantially equal size, and the thirdelectrode occupies more area in the third cell than the third electrodeoccupies in the fourth cell. The fourth electrode is disposed on thesubstrate and extends through the third and fourth cells. The fourthelectrode occupies more area in the fourth cell than the fourthelectrode occupies in the third cell. The controller detects a force anda position of the force based on signals communicated by the forcesensor circuit. The first track couples the first electrode to thecontroller. The second track couples the second electrode to thecontroller. The third track couples the third electrode to thecontroller. The fourth track couples the fourth electrode to thecontroller. The first cell contains only four electrodes. Each of thefirst, second, third, and fourth electrodes include a plurality offingers extending from a body.

Embodiments of the present disclosure provide one or more technicaladvantages. For example, one embodiment reduces the number of tracksused to implement force sensing. As another example, one embodimentdetects a position of a force using a force sensor that has only fourelectrodes. Certain embodiments of the invention may include none, some,or all of the above technical advantages. One or more other technicaladvantages may be readily apparent to one skilled in the art from thefigures, descriptions, and claims included herein.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other computer-readablenon-transitory storage media, or any combination of two or more ofthese. A computer-readable non-transitory storage medium may bevolatile, non-volatile, or a combination of volatile and non-volatile.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.Additionally, components referred to as being “coupled” includes thecomponents being directly coupled or indirectly coupled.

This disclosure encompasses a myriad of changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Similarly, where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative.

1-20. (canceled)
 21. An apparatus comprising: a force sensor circuitcomprising: a substrate; a first electrode disposed on the substrate,the first electrode extending through first and second cells of a row ofcells, and the first electrode occupying more area in the first cellthan the first electrode occupies in the second cell; a second electrodedisposed on the substrate, the second electrode extending through thefirst and second cells, the second electrode occupying more area in thesecond cell than the second electrode occupies in the first cell; athird electrode disposed on the substrate, the third electrode extendingthrough third and fourth cells of a column of cells, and the thirdelectrode occupying more area in the third cell than the third electrodeoccupies in the fourth cell; and a fourth electrode disposed on thesubstrate, the fourth electrode extending through the third and fourthcells, the fourth electrode occupying more area in the fourth cell thanthe fourth electrode occupies in the third cell; and a controllerconfigured to detect a force and a position of the force based onsignals communicated by the force sensor circuit.
 22. The apparatus ofclaim 21, further comprising: a first track coupled to the firstelectrode; a second track coupled to the second electrode; a third trackcoupled to the third electrode; and a fourth track coupled to the fourthelectrode.
 23. The apparatus of claim 21, wherein the controller isconfigured to detect the position of the force based on: a first ratioof a first signal of the first electrode and a second signal of thesecond electrode; and a second ratio of a third signal of the thirdelectrode and a fourth signal of the fourth electrode.
 24. The apparatusof claim 21, wherein each of the first, second, third, and fourthelectrodes comprise a plurality of fingers extending from a body. 25.The apparatus of claim 24, wherein a first finger of the plurality offingers of the first electrode is a different length than a secondfinger of the plurality of fingers of the first electrode, the firstfinger in the first cell and the second finger in the second cell. 26.The apparatus of claim 21, where in the controller is further configuredto: determine a horizontal position of the force based on signals of thefirst and second electrodes of the first cell; and determine a verticalposition of the force based on signals of the third and fourthelectrodes of the third cell.
 27. The apparatus of claim 21, wherein:the first and second electrodes of the first cell are disposed on afirst surface of the substrate; and the third and fourth electrodes ofthe first cell are disposed on a second surface of the substrate. 28.The apparatus of claim 21, wherein the first cell contains only fourelectrodes.
 29. The apparatus of claim 21, wherein the first and secondelectrodes occupy substantially the same amount of area as the third andfourth electrodes.
 30. The apparatus of claim 21, wherein an amount ofarea occupied by the first and second electrodes in the row of cells issubstantially the same amount of area occupied by the third and fourthelectrodes in the column of cells.
 31. A force sensor comprising: asubstrate; a first electrode disposed on the substrate, the firstelectrode extending through first and second cells of a row of cells,and the first electrode occupying more area in the first cell than thefirst electrode occupies in the second cell; a second electrode disposedon the substrate, the second electrode extending through the first andsecond cells, the second electrode occupying more area in the secondcell than the second electrode occupies in the first cell; a thirdelectrode disposed on the substrate, the third electrode extendingthrough third and fourth cells of a column of cells, and the thirdelectrode occupying more area in the third cell than the third electrodeoccupies in the fourth cell; and a fourth electrode disposed on thesubstrate, the fourth electrode extending through the third and fourthcells, the fourth electrode occupying more area in the fourth cell thanthe fourth electrode occupies in the third cell.
 32. The force sensor ofclaim 31, wherein: the first and second electrodes extend through thethird and fourth cells; and the third and fourth electrodes extendthrough the first and second cells.
 33. The force sensor of claim 31,further comprising: a first track coupled to the first electrode; asecond track coupled to the second electrode; a third track coupled tothe third electrode; and a fourth track coupled to the fourth electrode.34. The force sensor of claim 31, wherein each of the first, second,third, and fourth electrodes comprise a plurality of fingers extendingfrom a body.
 35. The force sensor of claim 34, wherein a first finger ofthe plurality of fingers of the first electrode is a different lengththan a second finger of the plurality of fingers of the first electrode,the first finger in the first cell and the second finger in the secondcell.
 36. The force sensor of claim 31, wherein: the first and secondelectrodes are disposed on a first surface of the substrate; and thethird and fourth electrodes of the first cell are disposed on a secondsurface of the substrate.
 37. The force sensor of claim 31, wherein thefirst cell contains only four electrodes.
 38. The force sensor of claim31, wherein the first and second electrodes occupy substantially thesame amount of area on the substrate as the third and fourth electrodes.39. The force sensor of claim 31, wherein an amount of area occupied bythe first and second electrodes in the row of cells is substantially thesame amount of area occupied by the third and fourth electrodes in thecolumn of cells.
 40. An apparatus comprising: a force sensor circuitcomprising: a substrate; a first electrode disposed on the substrate,the first electrode extending through first and second cells of a row ofcells, and the first electrode occupying more area in the first cellthan the first electrode occupies in the second cell; a second electrodedisposed on the substrate, the second electrode extending through thefirst and second cells, the second electrode occupying more area in thesecond cell than the second electrode occupies in the first cell; athird electrode disposed on the substrate, the third electrode extendingthrough third and fourth cells of a column of cells, and the thirdelectrode occupying more area in the third cell than the third electrodeoccupies in the fourth cell; and a fourth electrode disposed on thesubstrate, the fourth electrode extending through the third and fourthcells, the fourth electrode occupying more area in the fourth cell thanthe fourth electrode occupies in the third cell; a controller configuredto detect a force and a position of the force based on signalscommunicated by the force sensor circuit; a first track coupling thefirst electrode to the controller; a second track coupling the secondelectrode to the controller; a third track coupling the third electrodeto the controller; and a fourth track coupling the fourth electrode tothe controller, wherein: the first cell contains only four electrodes;and each of the first, second, third, and fourth electrodes comprise aplurality of fingers extending from a body.